1. Field of the Invention
The present invention relates to an optical fiber and an optical transmission system.
2. Description of the Related Art
With the recent dramatic increase in the Internet traffic, it is expected that transmission capacity will be insufficient in the future. As methods for solving this, mode-division-multiplexing transmission techniques are disclosed in which higher-order propagation modes are used for optical transmission in addition to a fundamental propagation mode of the optical fiber that has been conventionally used (refer to C. Koebele, M. Salsi, G. Charlet, S. Bigo “Nonlinear Effects in Long-Haul Transmission over Bimodal Optical Fiber,” ECOC2010, Mo.2.C.6. and Bernd Franz, Detlef Suikat, Roman Dischler, Fred Buchali, Henning Buelow “High Speed OFDM Data Transmission Over 5 km GI-Multimode Fiber Using Spatial Multiplexing With 2×4 MIMO Processing,” ECOC2010, Tu.3.C.4.). For higher quality optical transmission, it is also important to enlarge an effective core area (Aeff) of the optical fiber so as to suppress the occurrence of a nonlinear optical phenomenon in the optical fiber (refer to Marianne Bigot-Astruc, Frans Gooijer, Nelly Montaigne, Pierre Sillard, “Trench-Assisted Profiles for Large-Effective-Area Single-Mode Fibers,” ECOC2008, Mo.4.B.1. and Yoshinori Yamamoto, Masaaki Hirano, Kazuya Kuwahara, Takashi Sasaki “OSNR-Enhancing Pure-Silica-Core Fiber with Large Effective Area and low Attenuation,” OFC/NFOEC2010, 0TuI2.). In Marianne Bigot-Astruc, et al., “125 μm glass diameter single-mode fiber with Aeff of 155 μm2” OFC/NFOEC2011, 0TuJ2 (2011), an optical fiber is proposed in which Aeff is enlarged to 155 μm2 by optimizing a refractive index profile using a trench structure.